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European iron ore production is primarily sourced from magnetite dominated iron oxide-apatite ore deposits in the northern Norrbotten ore province of northernmost Sweden. The Malmberget iron oxide-apatite deposit is at present the largest iron ore resource in Europe and is an amphibolite facies grade analogue of the world-famous Kiirunavaara iron oxide-apatite deposit. The Malmberget rock association is characterised by multiple phases of deformation, metamorphism, and alteration that resulted in a geometrically and petrologically complex deposit that is genetically ambiguous. Primary ore textures and emplacement structures of the Malmberget iron oxide-apatite deposit have largely been recrystallised during metamorphic overprinting and now comprise dominantly medium- to coarse-grained granoblastic magnetite. However, isotopic characteristics are preserved and when combined with trace element chemistry, these can be used to understand magmatic vs. hydrothermal origin of the deposit. To unravel the primary origin of the Malmberget magnetite ore, we combined magnetite trace element chemistry and Fe-O stable isotopes to investigate the massive magnetite in the Fabian-Kapten and ViRi ore bodies of the Malmberget iron oxide-apatite deposit. Trace element correlations indicate a high-temperature magmatic to a transitional high-temperature magmatic-hydrothermal origin of the Malmberget iron oxide-apatite ore deposit, with data plotting into fields of clear magmatic affinity in trace element discrimination diagrams. Fe-O data fall into established magmatic fields regardless of subsequent metamorphic modifications, underlining a dominantly (ortho-)magmatic origin of the investigated deposits. Despite an overall magmatic to magmatic-hydrothermal origin for the two ore bodies studied, Fe-O isotope equilibrium calculations of the magnetite suggest a possible temperature discrepancy between the Fabian-Kapten ore body and the ViRi ore body, the latter showing a more pronounced magmatic character. These variations in trace element contents and Fe-O isotopes can be explained by the proximity of the more magmatic signatures to the centre of the ore forming magmatic system.

Our primary purposes are to determine the genesis and the main source rocks that provide the magnetite on the beaches, as well as the compatible and discriminate elements of the studied magnetite using the multivariate diagram and principal component analysis (PCA). Optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) are primarily used to evaluate the purity of magnetite grains, and laser ablation–inductively coupled plasma–mass spectrometry is primarily used to determine the chemical composition of magnetite. In this study, two types of magnetite were distinguished, namely magmatic magnetite and hydrothermal magnetite. To determine the compatible and discriminant variables, three steps were performed. In the first step, the number of variables was reduced using a multivariate diagram. The results revealed that Zn, P, Ca, Cr, Cu, Na, and K, and Fe, Mg, Al, Ti, V, Mn, Co, Sc, Ni, Ga, Zr, Nb, and Sn served as compatible variables in magmatic and hydrothermal magnetite, respectively. In the second step, box-and-whisker plots, hierarchical clustering, and variable importance in projection (VIP) plots were used to identify discriminant variables based on the aforementioned compatible elements. The results indicated that in both hydrothermal and magmatic magnetite, Fe, Al, Ti, Mg, Mn, V, and Zn served as highly discriminant variables, while Zr, Sn, Sc, and Nb served as poorly discriminant variables. Other elements such as Co, Cr, Cu, Ca, Ga, Ni, K, and Na exhibited varying discriminant values. In the third step, the discriminant variables determined in the second step were arranged using the ranking model of PCA for each study sample. In conclusion, multivariate plots, box-and-whisker plots, VIP plots, and PCA are useful tools for determining the compatible and discriminant elements of magnetite. [ABSTRACT FROM AUTHOR]

The Dalli porphyry Cu-Au deposit is located in the central parts of Urumieh –Dokhtar Magmatic Arc (UDMA). This deposit is formed via the emplacing of Miocene intrusions mainly containing diorite and quartz diorite within the Eocene andesite and porphyritic basaltic andesite units. Main alterations in this region include potassic, propylitic and to a lesser extent phyllic. In this study, magnetite chemistry in the potassic alteration zone is investigated. The results of EMPA show that magnetites of this Au-rich porphyry system are characterized by enrichment in Ti, Al, V, Mg, and Mn values. Also, the magnetites formed via the hydrothermal processes. Evidences such as magnetite martitization and exsolution of ilmenite lamellae imply for magnetite crystallization in high oxygen fugacity conditions. Moreover, based on the Al + Mn vs. Ti + V diagram studied magnetites follow the trend of temperature decreasing which could be considered as an important factor in increasing the potentials of sulfide mineralization thorough the hydrothermal system evolution. Compared with Daralou and Regan porphyry systems, the Dalli magnetites contain higher concentrations of Ni, Mn, Cr, and Co presenting an exploration key for discovering the Au-rich porphyry deposits. Introduction Porphyry copper deposits (PCDs) are related to the shallowly emplaced (5-10 km) oxidized magmatic systems in the subduction, syn-collisional, as well as post-collisional tectonic settings (Richards, 2011). They supply most of the world's Cu and Mo resources; ~80 % Cu and ~95 % Mo (Sun et al., 2015). In Iran, widespread occurrence of porphyry copper deposits has been discovered and mined in the Urumieh-Dokhtar Magmatic Arc (UDMA; Richards, 2015). These deposits are related to the evolution of the Neo-Tethys ocean starting with subduction in late Cretaceous to middle Miocene and subsequent prevailing the syn- to post-collisional tectonic regimes during the Neogene (Richards, 2015; Zarasvandi et al., 2018). Most of the porphyry bearing intrusions of UDMA exhibiting a spectrum of mineralization from weakly to highly mineralized systems were emplaced during the Miocene (e.g., Sarcheshmeh, Meiduk, and Dalli). Recent studies concerning on the source of mineralized porphyry granitoids in the UDMA (e.g., Asadi, 2018) specified a model comprising the partial melting of subduction-modified thickened mafic juvenile lower crustal rocks responsible to generation of adakite-like-hydrous, relatively oxidized magmas (Sun et al., 2015) with the high potential to form porphyry Cu ± Mo ± Au systems. During the last decade, magnetite geochemistry has been the focus of several studies trying to constrain the physicochemical attributes of igneous and hydrothermal ore systems (e.g., Dare et al. 2014). Magnetite can form under various conditions having the capability of fixing various minor and trace elements (e.g., Co, Cr, V, Ti, Mn, Mg, and Al) in its spinel structure (Nadoll et al., 2015). This makes magnetite able to record many environmental variables which are very important in mineralization potential of porphyry Cu-systems (e.g., oxygen fugacity, temperature, and ratios of fluid-rock interaction). Although the Dalli porphyry Cu-Au deposit has been the subject of many studies manly focusing on the magmatic evolution, fluid inclusion, silicate (plagioclase, biotite, and amphibole) and sulfide (pyrite and chalcopyrite) chemistry (Ayati et al., 2013; Zarasvandi et al., 2015a; Zarasvandi et al., 2018; Zarasvandi et al., 2019c); none focused on the oxide minerals (magnetite composition). The present work reports petrographic and chemical data of magnetite and tries to constrain the factors controlling the formation of Dalli deposit. Material and Methods Sampling was carried out on drill cores and special care was undertaken to select the samples showing no obvious overprint of low temperature alteration. Polished thin sections were prepared from 1-2 cm sized blocks for microscopy and electron probe microanalyzer (EPMA) studies. Wavelength-dispersive (WDS) EPMA analyses of oxides were conducted at the Chair of Resource Mineralogy, Montanuniversität Leoben, Austria using the Jeol JXA 8200 instrument and the following analytical conditions: 15 kV accelerating voltage, 10 nA beam current and beam size to spot mode (of about 1μm). K lines were used for Mn, Fe, Ti, Mg, Al, Cr, and V. The counting times for element peaks and background (upper and lower) were 100 s and 20 s, respectively. The lower limit of detection for these elements (single standard deviation) as calculated by the integrated Jeol software. Results In the Dalli porphyry Cu-Au deposit, hypogene mineralization mostly includes pyrite, chalcopyrite, and magnetite with minor chalcocite and bornite. Ore minerals occur as aggregates, in veinlets or disseminations within the potassic alteration, and to a lesser extent in the phyllic alteration zones. In the all analyzed samples, the values of Al2O3, V2O3 and MnO were upper then detection limit. Conformably, detectable values were mainly obtained for TiO2, Cr2O3 and MgO. On the contrary NiO, SiO2, CuO were mainly below the detection limit. The FeO content (wt. %) in the analyzed magnetites varies between 91.01 to 98.57 (average; 97.01), Al2O3 between 0.063 -5.07 wt. % (average 0.62 wt. %), and the lowest and highest values of V2O3 are 0.02 and 0.34 (wt. %), respectively. The average of MnO and MgO in the analyzed samples is 0.25 and 0.07 (wt. %), respectively. Additionally, the TiO2 content varies between 0.01 and 2.45 (wt. %); averaging 0.34 (wt. %). Discussion On the Ti (ppm) vs. V (ppm) discrimination diagram, most of the analyzed magnetites extended to the field of hydrothermal field providing insight into the formation of magnetite owing to the exsolving of hydrothermal fluids through the potassic alteration. Comparison of the magnetite composition in the Dalli deposit with other PCDs in the UDMA implies that there are higher average contents (wt. %) of Mn, Fe, Mg, and Cr compared with Daralou (an example of pre-collisional porphyry intrusion) and Keder porphyry systems (an example of weakly mineralized collisional porphyry deposit). These features may highlight the importance of magnetite composition in establishing the discrimination diagrams of Au-rich porphyry Cu-deposits using magnetite composition. The documented oxy-exsolution of ilmenite as well as hematite intergrown with magnetite in the Dalli samples are the indicative of high in the potassic alteration stage. Under such highly oxidized conditions sulfur is present as oxidized species (such as ) rather than as reduced species (such as ) preventing the extensive sulfide deposition in magmatic and early stages of potassic alteration (Zarasvandi et al., 2022). This process could enhance the mineralization potential of the system by preserving the sulfur content, especially before the main mineralization stages. Besides optimum tectonomagmatic conditions, the physicochemical attributes of potassic alteration may also have a decisive role in predicting the mineralization potential of porphyry systems (Zarasvandi et al., 2018). Because bulk sulfide mineralization occurs at the end of potassic alteration (Richards, 2011). Prevailing of the high temperatures in potassic alteration could prevent the disproportion SO2 to H2S which is necessary for sulfide precipitation (Richards et al., 2017; Zarasvandi et al., 2018). Conformably, the inability of hydrothermal systems for cooling could be linked to the low mineralization degree of the porphyry deposits. Based on the Al + Mn vs. Ti + V diagram (Zhao et al., 2018), samples of Dalli deposit follow the trend of temperature decreasing which indicate the desirable conditions for enhancing the sulfide mineralization in the Dalli porphyry Cu-Au deposit.

The Dalli porphyry Cu-Au deposit is located in the central parts of Urumieh –Dokhtar Magmatic Arc (UDMA). This deposit is formed via the emplacing of Miocene intrusions mainly containing diorite and quartz diorite within the Eocene andesite and porphyritic basaltic andesite units. Main alterations in this region include potassic, propylitic and to a lesser extent phyllic. In this study, magnetite chemistry in the potassic alteration zone is investigated. The results of EMPA show that magnetites of this Au-rich porphyry system are characterized by enrichment in Ti, Al, V, Mg, and Mn values. Also, the magnetites formed via the hydrothermal processes. Evidences such as magnetite martitization and exsolution of ilmenite lamellae imply for magnetite crystallization in high oxygen fugacity conditions. Moreover, based on the Al + Mn vs. Ti + V diagram studied magnetites follow the trend of temperature decreasing which could be considered as an important factor in increasing the potentials of sulfide mineralization thorough the hydrothermal system evolution. Compared with Daralou and Regan porphyry systems, the Dalli magnetites contain higher concentrations of Ni, Mn, Cr, and Co presenting an exploration key for discovering the Au-rich porphyry deposits. [ABSTRACT FROM AUTHOR]

The geochemistry of magnetite provides constraints on the source(s) of the magnetite and other ore minerals. In this study, we constructed a magnetite distribution map, compared the chemical composition of magnetite present in hard rocks with that present in sand beach and stream deposits to determine magnetite's provenance, investigated relationships among different trace elements, examined variations in the concentrations of trace elements present in magnetite, and identified the type of studied magnetite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry/inductively coupled plasma atomic emission spectroscopy was used to analyze samples available in small and large amounts, respectively. The average magnetite compositions of beach and river samples were substantially similar to those of andesite rocks, revealing that the magnetite samples may have originated from surrounding andesite rocks; this finding is consistent with the chemical composition of the samples analyzed using LA-ICP-MS. Some of the andesite rocks found in the study area were the primary source of magnetite aggregations in the beach sands and stream sands near or slightly away from these rocks. High Ti–V magnetites lie within the fields of Fe–Ti–V bearing magnetite and titanomagnetite (ulvöspinel). These titanomagnetites may be undergoing transformation to spinel minerals such as galaxite, gahnite, magnesiochromite, and chromite, which are characterized by the high concentrations of Al, Ti, Mg, Cr, Ni, Mn, and Zn. The positive correlation between Fe and Ti, Cr and Ni, and also the negative correlation between Fe and Mg, Mn and Zn can be attributed to various magnetite phases present in the study area. V, Co, Mo, Nb, Ga, Sn, and Ta exhibited a positive correlation with Fe and a negative correlation with Al. The positive correlation between Fe and these elements indicates the enrichment of these elements in the magnetite series. We observed a negative correlation between Fe and Li, Rb, Ca, Ba, Sr, Cu, Cd, Sb, As, Sc, Y, REE, U, and Th. A positive correlation between Al and these elements indicates the enrichment of these elements in the spinel series. [ABSTRACT FROM AUTHOR]

[Display omitted] • Studied magnetite distribution on Taiwan's eastern and western beaches using magnetite concentrations in beach sands. • Investigated geochemical compatibility and discrimination elements in the magnetite crystal structure. • Unraveled magnetite provenance and genesis to target possible mining locations. This study investigated the compatible and discriminant elements of magnetite in rocks and beach sands on Taiwan's western and eastern shores. Scanning electron microscopy, X-ray diffraction, and optical microscopy were used to evaluate the purity of the studied magnetite grains, while laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-Ms) was used to determine the chemical composition. Multivariate diagrams and principal component analysis (PCA) were also used to better determine Taiwan's magnetite resource and mining potential. Two types of magnetite were identified in this study: primary magmatic and hydrothermal. Three steps were followed to determine the compatible and discriminant variables. In the first step, a multivariate diagram was used to reduce the number of variables. The results revealed that Zn, P, Ca, Cr, Cu, Na, and K, as well as Fe, Mg, Al, Ti, V, Mn, Co, Sc, Ni, Ga, Zr, Nb, and Sn, were compatible variables in magmatic and hydrothermal magnetite, respectively. In the second step, box-and-whisker plots, hierarchical clustering, and variable importance in projection (VIP) plots were used to identify discriminant variables based on the aforementioned compatible elements. The results indicated that Fe, Al, Ti, Mg, Mn, V, and Zn were highly discriminant variables. In contrast, Zr, Sn, Sc, and Nb were low discriminant variables in hydrothermal and magmatic magnetite. Other elements, such as Co, Cr, Cu, Ca, Ga, Ni, K, and Na, exhibited varying discriminant values. The discriminant variables obtained from the second step were arranged using the PCA ranking model for each study sample in the third step. In summary, multivariate diagrams, box-and-whisker plots, VIP plots, and PCA were useful tools for determining magnetite-compatible and discriminant elements. Regarding its resource potential, Taiwanese magnetite was found to be of high grade (>65%), suitable for manufacturing pig, cast, wrought, and steel iron based on its Mn content. Finally, this study highlighted the magnetite resource potential of andesite, migmatite, and serpentinite units exposed at the surface. Exploration and evaluation of these units are strongly recommended. [ABSTRACT FROM AUTHOR]

• Facile, one-pot method to synthesize ferrite nanoparticles at near-ambient conditions. • Regardless of precursor used, the final morphology, structure, and size of the ferrite nanoparticles remains identical. • Ferrite nanoparticles produced show sound magnetic properties and can be a proof-of-concept to further explore our synthesis procedure. Herein we describe a new, quite simple, highly scalable, one-pot protocol for the synthesis of ferrite nanoparticles, NPs. We immerse water insoluble iron boride, FeB, powders – in plastic bottles at temperatures between 50 °C and 80 °C and ambient pressures – for tens of hours in high pH aqueous solutions of potassium-, sodium-, tetramethylammonium-, or tetrabutylammonium-hydroxides. The resulting powder is comprised of iron oxide, Fe 3 O 4 , NPs with, in one case, a saturation magnetization of 75 Am2kg−1, that exhibit ferrimagnetic behavior, with a critical temperature of 820 K. The same protocol was used to convert water soluble iron sulphate, FeSO 4 , to the same NPs. The average size of the NPs depends on reaction time; after 24 h, they are in the 15 nm range; after 48 h, they are closer to 25 nm. While our approach may appear to be similar to the co-precipitation method for making such NPs, we make a strong case that our approach is significantly simpler, nonetheless reaching high magnetization of NPs. [ABSTRACT FROM AUTHOR]

Introduction There is an iron mining complex called Shahrak 60 km east of Takab town, NW Iran. The exploration in the Shahrak deposit (general name for all iron deposits of the area) started in 1992 by Foolad Saba Noor Co. and continued in several periods until 2008. The Shahrak deposit comprising 10 ore deposits including Korkora-1, Korkora-2, Shahrak-1, Shahrak-2, Shahrak-3, Cheshmeh, Golezar, Sarab-1, Sarab-2, and Sarab-3 deposits )Sheikhi, 1995) with total 60 million tons of proved ore reserves. The Fe grade ranges from 45 to 65% (average 50%). The ore reserves of these deposits vary and the largest one is Korkora-1 with 15 million tons of 55% Fe and 0.64% S. The Korkora-1 ore deposit is located in western Azarbaijan and Urumieh-Dokhtar volcanic zone, at the latitude of 36°21.8´, and longitude of 47°32´. Materials and methods Six thin-polished sections were made on magnetite, garnet, and amphibole for EPMA (Electron Probe Micro Analysis). EPMA was performed using a JEOL JXA-733 electron microprobe at the University of New Brunswick, Canada, with wavelength-dispersive spectrometers. Results and discussion Outcropped units of the area are calc-alkaline volcanics of rhyolite, andesite and dacite and carbonate rocks of Qom Formation in which intrusion of diorite to granodiorite and quartzdoirite caused contact metamorphism, alteration plus skarnization and formation of actinolite, talc, chlorite, phlogopite, quartz, calcite, epidote and marblization in the vicinity of the ore deposit. Iron mineralization formed at the contacts of andesite and dacite with carbonates in Oligo-Miocene. The study area consists of skarn, metamorphic rocks, and iron ore zones. The shape of the deposit is lentoid to horizontal with some alteration halos. The ore occurred as replacement, massive, disseminated, open-space filling and breccia. The ore minerals of the deposit include low Ti-magnetite (0.04 to 0.2 wt % Ti), minor apatite, and sulfide minerals such as pyrite and chalcopyrite. Magnetite is the most important mineral and has 0.2 to 4 mm grain size and partly transformed into hematite, limonite and goethite. In some places, magnetite can be seen as euhedral grains in hand specimen. Supergene minerals such as chalcocite, malachite, azurite, and covellite are also present. Hematite formed as primary and secondary types in which primary type occurred in deeper parts of the ore body along with magnetite and has lamellar texture with up to 0.2 mm grain size. Meanwhile, secondary type of hematite formed from martitization along magnetite grain boundaries and fractures. In the surface area of the deposit, ore minerals strongly altered to mixtures of oxide and hydroxide minerals (ochre) like goethite, hematite, limonite and lepidochrocite which changed the color of the ore body to yellow, deep orange, red and brown. Pyrite is the most important sulfide mineral and formed in three stages. In the first stage, pyrite occurred with magnetite and has 0.1 to 0.3 mm subhedral to anhedral grains which altered to oxide and hydroxide minerals. At the second stage, pyrite has 0.2 to 1 mm euhedral grains, occurred between the magnetite and gangue minerals and converting to chalcopyrite. At the third stage, pyrite with magnetite, calcite and quartz filled fractures as open-space fillings and are pretty unaltered. The skarn zone includes garnet, pyroxene, secondary calcite, epidote, and chlorite and the metamorphic zone includes marble. Sericitization, silicification, calcitization, chloritization-epidotization, argilitization, propylitization and actinolitizion are the important alterations in the area from which chloritization-epidotization and calcitization in the ore and propylitic alteration in the volcanics are dominant. The EPMA analytical results on 30 points on magnetite and hematite suggest that the amount of Ti and V (0.004 wt % and 0.002 wt % in average, respectively) are low in contrary to Mn and Al (0.33 wt % and 5.32 wt % in average, respectively). Therefore, it fits in the skarn ore deposit domain in Ni/(Cr + Mn) versus Ti + V and Ca + Al + Mn versus Ti + V discrimination diagrams of iron ore deposits (Beaudoin et al., 2007). High Mn in the rock samples of Korkora-1 can be resulted from substitution of Fe+2 by Mn+2 in magnetite structure that can be a sign of hydrothermal skarn. Titanium, Mn, V and Zn show a positive correlation and Al, Cu, Mg, P, Si, Ca, Ni and Cr show a negative correlation with Fe. According to the chemistry of magnetite and plotting them on V2O5 versus TiO2 and V2O5 versus Cr2O3 diagrams, it can be recognized that the samples of Korkora-1 deposit resemble exoskarn magnetite of Goto deposit. The analysis of goethite of Korkora-1 show the amount of 2.5 to 4 wt % SiO2, 76 wt % Fe, and Ni (110 ppm) without Ti and Cr in its structure. Mineralographical and geochemical evidence from ore, occurrence of iron in contact with carbonates and skarn mineralogy such as garnet, pyroxene, secondary calcite, epidote and chlorite suggest iron skarn genesis for Korkora-1 deposit. Fluids generated from intrusive bodies like diorite and quartz-diorite with variations in physicochemical conditions, produced skarn in contact with carbonates and volcanic rocks. The heat from intrusive bodies caused recrystallization of carbonates and formed marbles in the footwall of the deposit. Meteoric water has also less important contribution in the ore-forming fluids. Fluid inclusion studies show existing of two types of fluids, a low salinity (10 wt % NaCl equiv.) and a medium salinity (25 to 30 wt % NaCl equiv.) fluid. Mixing magmatic and meteoric waters makes decreasing in the temperatures and deposition of ore fluids. The Korkora-1 deposit formed in four stages: 1) intruding the intrusive bodies, 2) entering Fe and SiO2 into Qom carbonates and forming calc-silicates, 3) mixing magmatic and meteoric fluids, hydrolysis of calc-silicates, consuming H+, instability of Fe complexes and deposition of iron oxides, 4) retrograde alterations of hydrous and non-hydrous calc-silicates with low temperature and high fO2 fluids and forming chlorite, calcite, clay minerals and hematite. Acknowledgements We gratefully thank Mr. Reza Sheikhi from Saba Noor Co. who kindly helped us during the research. We also thank Professor David Lentz from University of New Brunswick for advising and supporting the research. References Sheikhi, R., 1995. Economic geology study of Shahrak Fe deposit, east of Takab. M.Sc. Thesis, Shahid Beheshti University, Tehran, Iran, 161 pp. (in Persian with English abstract) Beaudoin, G., Dupuis, C., Gosselin, P. and Jebrak, M., 2007. Mineral chemistry of iron oxides: application to mineral exploration. In: C.J. Andrew (Editor), Ninth Biennial SGA meeting, SGA, Dublin, pp. 497−500.

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China. Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate). Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and f O 2 , may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of f O 2 , but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO 2 –Al 2 O 3 –(MgO + MnO) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed. [ABSTRACT FROM AUTHOR]

Magnetites of the Varėna Iron Ore Deposit (VIOD) were thoroughly investigated by the Cameca SX-100 microprobe at the Warsaw University and by the Quanta 250 Energy Dispersive Spectroscopy (EDS) at the Nature Research Centre in Vilnius, Lithuania. Four generations of magnetite were distinguished in the studied serpentine-magnetite ores (D8 drilling). The earliest, spinel inclusion-rich magnetite cores (Mag-1) might have formed during an early metamorphism and/or related skarn formation. They have the highest trace element (Si, Al, Mg, Ti, V, etc.) contents. Voluminous second magnetite (Mag-2) had replaced olivine, pyroxenes, spinel and other skarn minerals at c. 540 °C (Mag-Ilm geothermometer) and has trace elements washed out by hydrothermal fluids. The latest magnetites (Mag-3 and Mag-4) originated from the late thermal reworking by dissolution-reprecipitation processes. Some of the latest magnetites (Mag-4) are mostly related to the sulfide veins. As concerning the origin of the studied magnetites, they have similar trace element abundances as skarn magnetites, are in general Ti-poor. The Mag-1 is more than twice richer in Mg than the porphyry and Kiruna type iron ores. A slight enrichment in Al, Ti and V because of spinel and ilmenite inclusions may have caused the earliest Mag-1 to resemble the porphyry type ores, while the secondary Mag-2 has Al, Ca and Mn contents as low as the Kiruna type ores. Even though there are no precise age constructions for the iron ore formation process, it may be related to metamorphic, metasomatic and later hydrothermal processes, the last of which is assumed to have occurred during the c. 1.50 Ga within-plate AMCG magmatism. [ABSTRACT FROM AUTHOR]

The Miocene Sarkuh porphyry Cu deposit is located in the southwestern part of Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. Compared with the neighboring giant Sarcheshmeh porphyry Cu deposit, this is a low-grade sub-economic porphyry Cu system (110 million tons @ 0.26 % Cu) characterized by an unusual abundance of magnetite. The present work tried to answer the question of whether or not there are differences in the hydrothermal system of Sarkuh, resulting in the lack of considerable mineralization. In this way, the mineral associations and EMPA data of magnetite were considered to distinguish the different stages of magnetite crystallization reflecting the magmatic-hydrothermal evolution of the Sarkuh deposit. They include (1) magmatic stage magnetite, including magnetite inclusions within primary silicate minerals (i.e., plagioclase and biotite), (2) pre-ore stage magnetite associated with potassic alteration assemblages, (3) main ore stage magnetite tightly associated with sulfide mineralization, and (4) late stage magnetite forming overgrowths on the sulfides. The results of EPMA analysis confirm that magnetite of these four stages differ in Mn, Fe, Ti, Mg, Al, Cr, and V concentrations. Higher V concentrations are found in the magmatic and pre-ore stages, whereas Al and Si reach the highest in the ore and late stages. Our data show that increasing fluid-rock interaction and changes in the oxygen fugacity, especially during the main ore stage extending to the late stage, are key factors controlling the trace element partitioning of magnetite. Most of ore stage magnetite formed at temperatures >500 °C and high temperatures prevailed during it. Magnetite crystallization after the main stage of sulfide mineralization accompanied by (partial) martitization indicate the increase of oxygen fugacity towards the late hydrothermal stage. This could explain why the ore and late stage magnetites show chemical similarities to those from sulfur-poor iron oxide copper‑gold (IOCG) deposits rather than porphyry deposits. • Sarkuh porphyry Cu deposit is characterized by unusual abundance of magnetite. • Four stages of magnetite crystallization could reflect the magmatic-hydrothermal evolution. • Al and Si reach the highest in the ore and late stages. • Ore and late stage magnetites show chemical similarities to sulfur-poor IOCG deposits. [ABSTRACT FROM AUTHOR]

Iron formations are valuable archives of sedimentary conditions and post-depositional events. However, geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism and deformation, hampering their use as records of regional geological events. This work focuses on strongly reworked magnetite-quartz-rich rocks from the São José do Campestre Massif, one of the oldest fragments of preserved crust in South America. The genetic classification of these magnetite-quartz-rich rocks is not straightforward because primary assemblages and textures were variably modified by granulite facies metamorphism during a regional Paleoproterozoic migmatization event. To address genetic ambiguities, we analyzed their magnetite and pyroxene chemistry, whole-rock geochemistry, and Sm-Nd isotopes. Magnetite chemistry indicates that pyroxene-poor iron formations (Type B) are low in trace elements such as Ti, Al, V, and Mn, suggesting a chemical similarity to iron formations elsewhere. In contrast, magnetites from pyroxene-enriched Type A iron formations are rich in trace elements and more akin to magnetite crystallized from higher temperature systems, such as skarn and IOCG. The 147Sm/144Nd of these rocks show substantial variation even at the outcrop scale, indicating a locally-controlled, highly heterogeneous mixture of Archean, Paleoproterozoic, and Neoproterozoic sources. Therefore, our geochemical tools point out to heterogenous signatures of these magnetite-quartz rocks and proxies compatible with both low and high-temperature conditions and age of deposition spanning sources from the Archean to the Neoproterozoic. We interpret that the studied São José do Campestre magnetite-quartz rocks represent Archean iron formations with original magnetite chemistry and isotopic signatures variably modified by metamorphism and by at least one deformation-related hydrothermal event. These results contrast with similar examples from China and Greenland where iron formations either preserved the magnetite chemistry or the primary isotopic signatures. Our study indicates that metamorphism can selectively affect chemical proxies used to study iron formations and undermine the genetic classification of iron ores. Thus, these proxies should be carefully applied in the interpretation of syn -depositional environments of polydeformed belts. [Display omitted] • Deformed quartz-magnetite rocks from the São José do Campestre Massif, NE Brazil. • Iron formations reworked in multiple crustal deformation events. • Magnetite chemistry reflects original IF compositions and metamorphic remobilization. • Sm-Nd isotopes register multiple events of mixing with younger crustal components. [ABSTRACT FROM AUTHOR]

The Nabeba high-grade iron deposit (Republic of the Congo) is hosted by banded iron formation (BIF) in the Ivindo Basement Complex, which lies in the northwestern part of the Congo Craton. The Nabeba BIF is intercalated with chlorite-sericite-quartz schist and comprises two facies (oxide and a carbonate-oxide). In this study, whole-rock and LA-ICP-MS magnetite geochemistry of the BIF was reported. Magnetite samples from both BIF facies had fairly similar trace element compositions except for the rare earth element plus yttrium (REE + Y) distribution patterns. The high V, Ni, Cr, and Mg contents of the magnetite in the Nabeba BIF could be ascribed to the involvement of external medium-high temperature hydrothermal fluids during their deposition in relatively reduced environment. The Post-Archean Australian Shale (PAAS)-normalized REY patterns of the Nabeba BIF magnetite were characterized by LREE depletion coupled with varying La and positive Eu anomalies. Processing of the information gathered from the geochemical signatures of magnetite and the whole-rock BIF suggested that the Nabeba BIF was formed by the mixing of predominantly anoxic seawater (99.9%) with 0.1% of high-temperature (>250 °C) hydrothermal vent fluids, similar to the formation mechanism of many Archean Algoma-type BIFs reported elsewhere in the world. [ABSTRACT FROM AUTHOR]

• Chemistry and Fe-O isotope variation of magnetite support a pure magmatic origin of Washan deposit. • Fe isotopes fractionate during magma immiscible and during fluid exsolution processes. • Fe isotopes can be used as discriminators to distinguish the magmatic and hydrothermal deposits. Although discriminating high temperature mineral systems, for example, magmatic- vs magmatic-hydrothermal origin Fe deposits, is challenging, the emerging Fe isotope systematics have shown good potentials to provide crucial information on resolving the problem. Here, Fe isotopes of multiple types of samples from one iron oxide-apatite (IOA) deposit and two skarn Fe deposits are measured, aiming to study their behaviors in high temperature magmatic and magmatic-hydrothermal environments. The primary observation of this study is that magnetite samples from high grade ores of magmatic origin IOA deposits has a heavier Fe isotopic signature relative to the associated igneous rocks, whereas a lighter Fe isotopic composition in magnetite samples from magmatic-hydrothermal origin skarn deposits relative to the causative intrusions. Another distinctive feature is that δ56Fe values of the causative intrusions in the magmatic origin IOA deposits are lighter than that of non-fertile intrusions, whereas the ore-associated intrusions of the magmatic-hydrothermal deposit are heavier in δ56Fe than that of non-fertile igneous rocks. The above two observed scenarios suggest that Fe isotope fractionation exists in both magmatic immiscibility and hydrothermal fluid exsolution processes. Magma immiscibility leads to heavy Fe isotope enrichment in immiscible Fe-rich melt phase, and resulting light Fe enrichment in Si-rich melt phase. Hydrothermal fluid exsolution results in lighter Fe isotope enrichment in the exsolved liquid phase, with a heavy Fe isotope enrichment in the residual magma. Fe isotopes behave in different ways in magmatic and magmatic-hydrothermal mineralization processes, which makes Fe isotopes an effective tool to discriminate mineral deposits of magmatic origin from those formed by magmatic-hydrothermal processes. [ABSTRACT FROM AUTHOR]

• Akesayi magnetite was occurred mainly during the retrograde skarn and oxide stages. • Akesayi comprises of banded (BO), disseminated (DO), primary (MO-1) and secondary massive (MO-2) magnetite. • Variable magnetite compositions controlled by multiple factors. • Magnetite compositions in skarn deposits are more variable than previously thought. The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite. Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18O V-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18O V-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO 2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought. [ABSTRACT FROM AUTHOR]

• High Cl content of the magmatic fluid forms Fe–chloride complexes at low pH that increases with increasing of temperatures and pressures. • Fe-bearing fluids saturate as neutralized (increasing pH) during reaction with carbonates and decreasing temperature (~300 °C) with influx (Mixing) of cooler meteoric water. • Decreasing geostatic pressure was likely a crucial control on magnetite saturation with Fe-rich hydrothermal fluids forming stockwork veins and dike-like fracture fillings. The economically significant Baba Ali iron ore deposit, is located in the Sanandaj-Sirjan zone, western Iran, is associated with diorite. The mineralization trends in a ENE-WSW direction with thickness that varies from 30 m up to 50 m and a length of about 250 m. The main mineral assemblages are massive magnetite, epidote, actinolite, tourmaline, quartz, calcite, and pyrite. Using different magnetite compositional discrimination diagrams, the low concentrations of Ti (0.11 wt%), Al (0.06 wt%), Cr (19.62 ppm), and Co (20.26) and high Ni/Cr ratios (6.34) are consistent with a hydrothermal origin, similar to typical skarn mineralization. The different elemental compositions of various magnetite generations might be due to an ore-forming fluid that initially a high-T magmatic hydrothermal character, then evolved to a lower temperture meteoric water dominated system. It seems that Fe-bearing saline fluids infiltrated the carbonate host rocks, causing high temperature, acid metalliferous fluids to become neutralized during reaction with carbonates, causing a decrease in iron solubility and saturating as a magnetite with increasing pH and decreasing the temperature. The close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility, triggering ore precipitation and replacement at relatively low temperatures (~300 °C), under reducing conditions. [ABSTRACT FROM AUTHOR]

• The Jatobá IOCG deposit is notable by its copper–nickel mineralization zones. • Magnetite-apatite bodies are related to syn -tectonic nickel mineralization. • Magnetite with ilmenite lamellas was formed at temperatures above 600 °C. • Halogen-rich minerals were formed from superheated and hypersaline fluids. • Bulk of chalcopyrite precipitates due to temperature decrease (<380 °C). The Jatobá deposit represents a specific portion of an Archean-Paleoproterozoic iron oxide–copper–gold system, notable due to its hydrothermal nickel-rich zones. Neoarchean mafic and acid volcanic rocks of the Itacaiúnas Supergroup host the mineralized zones. Pre-, syn- and late shearing hydrothermal alteration, associated with the Canaã shear zone development, was pervasive and intense. Early distal hydrothermal alteration encompasses potassic-iron-silica (quartz–biotite–magnetite–apatite), sodic (albite, scapolite), and sodic-calcic (ferro-pargasite) alteration. The main syn -tectonic hydrothermal alteration stage resulted in scapolite–hastingsite–biotite controlled by the mylonitic foliation. Syn-deformation massive magnetite bodies represent proximal envelopes of the mineralized zones. They were intercepted by actinolite-apatite-magnetite and potassic-iron (biotite–magnetite) alteration fronts. Late tectonic hydrothermal alteration comprises chlorite–(epidote–quartz–calcite), fibrous scapolite veins, and green biotite–scapolite–F-Cl-apatite veinlets. The copper–(nickel) mineralized zones in the Jatobá deposit were formed in four stages, coeval to ductile and ductile-brittle deformational events. The mineralization stage (I), spatially related to massive magnetite–(apatite–actinolite) bodies, has the highest nickel content. It is characterized by Ni-pyrrhotite, Ni-pyrite, and subordinately, Co-chalcopyrite, Ce-allanite, Co-pentlandite, and Ce-monazite. The mineralization style evolved from replacement fronts controlled by the mylonitic foliation to hydraulic breccia zones. The mineralization stage (II) was synchronous to the development of syn -tectonic potassic-iron alteration and Co-chalcopyrite (±Ni-pyrite ± Ni-pyrrhotite). The mineralization stage (III), controlled by ductile-brittle and brittle structures, enabled the formation of veins with typical open-space filling textures infilled by paler brown or green biotite, Co-chalcopyrite, and siegenite (±Co-pyrite, ±Co-magnetite, ± cassiterite). The late mineralization stage (IV), coeval to widespread chlorite alteration, formed the most important copper mineralization at Jatobá. It is represented by branching veinlets and breccias with chalcopyrite, Co-chalcopyrite, Co-pyrite, sphalerite, molybdenite, uraninite, monazite, W-bearing hematite, and rare earth carbonates (bastnäsite, coskrenite, and sahamalite). The high chlorine contents of halogen-rich minerals (e.g., scapolite, biotite, apatite, and amphibole) imply the participation of highly saline, supersaturated fluids in the system evolution. Metalliferous fluids were highly focused, and mineralized zones represent the hotter hydrothermal centers. The high V and Ti contents in magnetite and its coexistence with hercynite and ilmenite indicate temperatures above 600 °C. These conditions would be similar to that of magnetite formed in the transition from magmatic to deep magmatic-hydrothermal systems, including the IOA deposits, especially on the onset of the early nickel-enriched mineralization stage. Such conditions enabled nickel leaching from mafic and mafic-ultramafic rocks, its transport in Cl-rich hydrothermal fluids, and precipitation related to episodic decompression. Temperature decrease (<380 °C), indicated by chlorite geothermometers, favored the bulk of chalcopyrite precipitation in late mineralization stages. The Jatobá deposit has attributes comparable to those of relatively deep portions of IOCG mineral systems formed from the channeling of overpressured superheated deep-seated fluids of probable magmatic origin. [ABSTRACT FROM AUTHOR]

• Two kinds of magnetite are identified at porphyry-related deposits in the Zhongdian region. • Some magnetite grains had undergone dissolution-reprecipitation processes. • The compositions of magnetite are affected by temperature, oxygen fugacity and hydrothermal alteration. The Zhongdian region in northwestern Yunnan (SW China) hosts a number of important porphyry and skarn deposits. In this study, we integrate petrographic observations, SEM-EDS elemental mapping, EPMA and LA-ICP-MS geochemical analyses on magnetite from several key deposits in the region. Magnetite grains from the Pulang porphyry Cu-Au, Lannitang porphyry Au-Cu, Langdu Cu skarn, Disuga porphyry, and andesite of Tumugou Formation were analyzed to unravel the magnetite formation mechanism, and the relative oxygen fugacity of the porphyry/skarn ore-related hydrothermal fluids in this region. Two types of magnetites (Magnetite I and II) have been identified. Magnetite I is commonly distributed in the chlorite and/or sericite alteration zone(s). Magnetite I grains are characterized by being textually inhomogeneous. The Magnetite I core (with local ilmenite exsolution lamellae) is Ti-Cr rich, indicative of a dominantly igneous origin. The Magnetite I core and its surrounding primary igneous minerals (biotite, amphibole and plagioclase) underwent late alteration. Magnetite I grains are characterized by core-rim texture, sharp core-rim contact, and irregular grain boundaries. These textural features indicate that Magnetite I may have undergone dissolution-reprecipitation processes, during which the Magnetite I core was chemically purified via losing Ti and gaining Fe. Magnetite II (in potassic and sericite alteration zones) is textually homogeneous with relatively low contents of Ti, Mg, Al, V, Ni, and Mn. We suggest that Magnetite II was formed by hydrothermal alteration. Compared to Magnetite II grains from the Pulang and Langdu deposits, those from the Lannitang deposit have lower Mn and V but higher Sn contents, indicative of higher oxygen fugacity of the hydrothermal fluids. We propose that binary plots such as Ti vs. Sc, V vs. Sn and Ga vs. Sn can distinguish the different origins of magnetites. From an exploration perspective, Magnetite II from the altered Disuga porphyries has similar texture and composition to its counterpart from the potassic-altered Pulang porphyries. This, together with the presence of Cu-sulfide inclusions in the Disuga Magnetite I, suggests significant mineralization potential in these porphyries. [ABSTRACT FROM AUTHOR]